Today's United States election will be decided by 10 swing states, regions where polling shows little distance between President Barack Obama and challenger Mitt Romney, a political scientist says.

Associate Professor Stephen Hoadley, of Auckland University, said much of the focus would be on Ohio because of its bellwether status. No presidential candidate has won in the past 50 years without taking it.

The other swing states are Colorado, Florida, Michigan, Nevada, New Hampshire, North Carolina, Pennsylvania, Virginia and Wisconsin.

In some of the state polls, just 0.3 of a per cent separates Mr Romney and the President. Latest polling puts Mr Obama ahead in Ohio, which carries 18 electoral college votes.

Professor Hoadley said: "In the north you've got industry, cars, steel mills, a lot of the rust belt - struggling industries that are having a lot of trouble competing with Asia.

"In and around Cincinnati you've got the intelligentsia and in the south there's a lot of farmers, a lot of Tea Party people. It's a north/south split.

"Generally speaking, Ohio tends to go Democrat."

One of the key states is Florida, which carries 29 electoral votes and has a mix of Hispanics, African Americans, whites and Jewish people.

The election would be decided in the middle - by voters who were neither dyed-in-the-wool Democrats nor Republicans, Professor Hoadley said. For those tending towards Romney, the economy loomed large.

"The slow recovery of the economy [some may think] anyone can promise a change. A lot of unemployed people who are desperate could say, 'Let's take a chance on the new guy - maybe he can make the economy bounce up again."'

Professor Hoadley's sister is in Ohio door-knocking for Mr Obama and making sure early votes are cast or that people can get to polling booths. The professor, who has been in New Zealand for 40 years and lectures in political studies, is also backing Mr Obama for a second term.

He said it was easy to get caught up in the contest from the other side of the world. "It's one of the greatest spectacles on earth. A lot of money will be spent, there will be a lot of hoopla. Everyone seems to be watching - it's going to be fascinating."